SPRINGFIELD — Illinois House Speaker Michael Madigan on Wednesday proposed making it tougher to approve increases in pension benefits for public workers throughout Illinois, an idea immediately opposed by the state's largest employee union.

The Democratic leader from Chicago introduced a state constitutional amendment that would ask voters this fall to require the Legislature to approve pension benefit increases by a three-fifths vote instead of a simple majority.

The stricter voting requirement also would apply to city halls, school districts and their retirement boards.

The measure would need to pass the House and Senate by early May for it to go before voters in November.

The move comes as the state of Illinois faces a yawning gap in public pension funding, and follows Tribune stories that have exposed how public officials and union members have padded pensions with lucrative sweeteners.

Madigan's proposal emerged only days before Democratic Gov. Pat Quinn is expected to reveal the fruits of a working group that has been debating how to rein in pension costs. The speaker's measure also could serve to soothe voter anger over burgeoning costs of public pensions.

Madigan's measure also would require a two-thirds vote for lawmakers to override a governor's veto or accept a governor's proposed changes in a rewrite of pension increase legislation. Currently, it takes a three-fifths vote to override an outright veto and only a simple majority to accept a governor's changes.

Madigan spokesman Steve Brown said the speaker's measure is aimed at making sure officials think about "what they're doing a little more seriously."

"It looks very favorable" but needs further review, said Roger Huebner, deputy executive director at the Illinois Municipal League.

But the breadth of the proposal drew the ire of theAmerican Federation of State, County and Municipal Employees. Anders Lindall, spokesman for the group representing state and local workers, said defects in pension laws that affect new state employees need to be fixed first. He also said the proposal would limit what issues could be bargained.

House Minority Leader Tom Cross, R-Oswego, also wants to require a third-party actuarial assessment before changes are made in pension laws, said Sara Wojcicki Jimenez, Cross' spokeswoman. She said House Republicans hope Madigan's proposal "is not his total answer for pension reform."